The disclosure of Japanese Patent Application No. 2000-187545 filed on Jun. 19, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to an internal combustion engine.
2. Description of Related Art
In a known internal combustion engine, an exhaust gas recirculation passage is provided for recirculating exhaust gas discharged from a combustion chamber into an intake passage of the engine. In such an internal combustion engine, as the amount of recirculation exhaust gas supplied into the combustion chamber is increased, the amount of soot produced gradually increases and reaches a peak. As the amount of recirculation exhaust gas supplied into the combustion chamber is further increased, the temperature of fuel and its surrounding gas upon combustion in the combustion chamber becomes lower than a temperature that allows soot to be produced, so that substantially no soot is produced. At the time of startup, this internal combustion engine performs a second mode of combustion in which the amount of recirculation exhaust gas supplied into the combustion chamber is less than the amount of recirculation exhaust gas that peaks the amount of soot produced. Subsequently, the engine performs a first mode of combustion in which the amount of recirculation exhaust gas supplied into the combustion chamber is greater than the amount of recirculation exhaust gas that peaks the production of soot and therefore substantially no soot is produced. An example of this internal combustion engine is described in, for example, Japanese Patent Application Laid-Open No. HEI 11-166435.
Japanese Patent Application Laid-Open No. HEI 11-166435 describes that at the time of start-up, the engine is warmed up by performing the second mode of combustion in order to activate a catalyst that controls exhaust gas discharged from the combustion chamber. However, this patent application does not disclose a method for preventing hydrocarbons present in exhaust gas from passing through the catalyst before the catalyst becomes able to remove hydrocarbons from exhaust gas. Therefore, Japanese Patent Application Laid-Open No. HEI 11-166435 also does not disclose that a means for accelerating the catalyst warm-up rate, after the catalyst has become able to control hydrocarbons present in exhaust gas, is provided during an operation for preventing hydrocarbons in exhaust gas from passing through the catalyst before the catalyst becomes able to control hydrocarbons in exhaust gas. In short, Japanese Patent Application Laid-Open No. HEI 11-166435 does not disclose a method for increasing the catalyst warm-up rate while preventing hydrocarbons from passing through the catalyst. Therefore, the internal combustion engine described in Japanese Patent Application Laid-Open No. HEI 11-166435 is not capable of quickly completing the warm-up of the catalyst while preventing hydrocarbons from passing through the catalyst, and is not capable of switching from the second mode of combustion to the first mode of combustion at an early time.
It is an object of the invention to provide an internal combustion engine capable of quickly completing the warm-up of a catalyst while substantially preventing passage of hydrocarbon through the catalyst, and of switching combustion from a second mode of combustion to a first mode of combustion at an early time.
In accordance with a first mode of the invention, an internal combustion engine has an exhaust gas recirculation passage for recirculating an exhaust gas discharged from a combustion chamber into an engine intake passage, wherein as an amount of a recirculation exhaust gas supplied into the combustion chamber is increased, an amount of a soot produced gradually increases and peaks. As the amount of the recirculation exhaust gas supplied into the combustion chamber is further increased, a temperature of a fuel and a surrounding gas upon combustion in the combustion chamber becomes lower than a temperature that allows the soot to be produced, so that substantially no soot is produced. At engine start-up, the engine first performs a second combustion in which the amount of the recirculation exhaust gas supplied into the combustion chamber is less than the amount of recirculation exhaust gas that peaks the amount of the soot produced. Then, the engine performs a first combustion in which the amount of recirculation exhaust gas supplied into the combustion chamber is greater than the amount of recirculation exhaust gas that peaks the amount of the soot produced, and substantially no soot is produced. The internal combustion engine includes an exhaust gas control catalyst for purifying the exhaust gas discharged from the combustion chamber. When the second combustion is performed at the start-up, the engine first curbs an amount of a hydrocarbon supplied to the exhaust gas control catalyst by performing a combustion in which the amount of the hydrocarbon in the exhaust gas does not increase, and a temperature of the exhaust gas discharged from the combustion chamber becomes relatively high. Then, the engine increases the amount of the hydrocarbon supplied to the exhaust gas control catalyst by performing a combustion in which the amount of the hydrocarbon in the exhaust gas increases, and the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high.
According to the internal combustion engine in the first mode of the invention, at the start-up, when performing, the second combustion in which the amount of the recirculation exhaust gas supplied into the combustion chamber is less than the amount of recirculation exhaust gas that peaks the amount of the soot produced, the engine first curbs the amount of hydrocarbon supplied to the exhaust gas control catalyst by performing the combustion in which the amount of hydrocarbon in exhaust gas does not increase, and the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high. That is, when the second combustion is performed at engine start-up, and the exhaust gas control catalyst has not become able to remove hydrocarbon from exhaust gas, the engine of the invention curbs the amount of hydrocarbon supplied to the exhaust gas control catalyst by performing the combustion in which the amount of hydrocarbon in exhaust gas does not increase. Therefore, the engine of the invention is able to prevent hydrocarbon in exhaust gas from freely passing through the exhaust gas control catalyst. Furthermore, while preventing hydrocarbon in exhaust gas from freely passing through the exhaust gas control catalyst before the exhaust gas control catalyst becomes able to remove hydrocarbon from exhaust gas, the internal combustion engine performs the combustion in which the temperature of exhaust gas discharged from the combustion chamber becomes relatively high. Thus, the temperature of the exhaust gas control catalyst is raised, i.e., a preparation for raising the temperature of the exhaust gas control catalyst is performed. As a result, the warm-up rate of the exhaust gas control catalyst, after the catalyst has become able to remove hydrocarbon from exhaust gas, can be increased.
Furthermore, the above-described internal combustion engine, while performing the second combustion at engine start-up, increases the amount of hydrocarbon supplied to the exhaust gas control catalyst by performing the combustion in which the amount of hydrocarbon in the exhaust gas increases, and the temperature of exhaust gas discharged from the combustion chamber becomes relatively high. This function is performed after curbing the amount of hydrocarbon supplied to the exhaust gas control catalyst by performing the combustion in which the amount of hydrocarbon in exhaust gas does not increase, and the temperature of exhaust gas discharged from the combustion chamber becomes relatively high. That is, after the exhaust gas control catalyst has become able to remove hydrocarbon from exhaust gas during the second combustion at the time of start-up, the engine raises the temperature of exhaust gas supplied to the exhaust gas control catalyst, and increases the amount hydrocarbon contained in the exhaust gas. Therefore, the duration between the time when the exhaust gas control catalyst becomes able to remove hydrocarbon from exhaust gas, and the time when the warm-up of the exhaust gas control catalyst is completed, can be reduced. Namely, the internal combustion engine of the first mode of the invention is able to quickly complete the warm-up of the exhaust gas control catalyst, while preventing hydrocarbon from freely passing through the exhaust gas control catalyst, and additionally accomplishes the switching from the second combustion to the first combustion at an early time.
In the first mode of the invention, it is possible to adopt a construction wherein, as the exhaust gas control catalyst, a recirculation exhaust gas control catalyst is disposed in the exhaust gas recirculation passage. Here, the engine sets the amount of the recirculation exhaust gas to zero when performing the combustion in which the amount of the hydrocarbon in the exhaust gas does not increase, and the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high. Furthermore, the engine gradually increases the amount of the recirculation exhaust gas when performing the combustion in which the amount of the hydrocarbon in the exhaust gas increases, and the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high.
According to this mode, during the second combustion at the start-up of the engine, when the engine performs the combustion in which the amount of the hydrocarbon in the exhaust gas does not increase, and the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high, the amount of recirculation exhaust gas is controlled to be zero. That is, the amount of recirculation exhaust gas is controlled to be zero before the recirculation exhaust gas control catalyst becomes able to remove hydrocarbon from recirculation exhaust gas during the second combustion at the time of start-up of the engine. Therefore, the engine is able to prevent problems that occur when the recirculation exhaust gas control catalyst is not able to remove hydrocarbon from recirculation exhaust gas, and recirculation exhaust gas is caused to flow through the exhaust gas recirculation passage, thus resulting in the clogging of the exhaust gas recirculation passage. Furthermore, while the amount of recirculation exhaust gas is controlled to be zero before the recirculation exhaust gas control catalyst becomes able to remove hydrocarbon from recirculation exhaust gas, the engine performs the combustion in which the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high. Therefore, a preparation for raising the temperature of the recirculation exhaust gas control catalyst can be performed. As a result, when recirculation exhaust gas is caused to flow through the recirculation exhaust gas control catalyst, high-temperature recirculation exhaust gas flows through the recirculation exhaust gas control catalyst. Therefore, the warm-up rate of the recirculation exhaust gas control catalyst after the catalyst has becomes able to remove hydrocarbon from recirculation exhaust gas can be increased.
Furthermore, the internal combustion engine, while performing the second combustion at the start-up, gradually increases the amount of recirculation exhaust gas when performing the combustion in which the amount of hydrocarbon in the exhaust gas increases, and the temperature of exhaust gas discharged from the combustion chamber becomes relatively high. This function is performed after controlling the amount of recirculation exhaust gas to be zero when performing the combustion in which the amount of hydrocarbon in the exhaust gas does not increase, and the temperature of exhaust gas discharged from the combustion chamber becomes relatively high. That is, after the recirculation exhaust gas control catalyst becomes able to remove hydrocarbon from recirculation exhaust gas during the second combustion at the start-up of the engine, the engine raises the temperature of recirculation exhaust gas supplied to the recirculation exhaust gas control catalyst, and increases the amount of hydrocarbon contained in the recirculation exhaust gas. Furthermore, the engine gradually increases the amount of recirculation exhaust gas. Therefore, the duration between the time when the recirculation exhaust gas control catalyst becomes able to remove hydrocarbon from recirculation exhaust gas, and the time when the warm-up of the recirculation exhaust gas control catalyst is completed, can be reduced. Namely, this engine is able to quickly complete the warm-up of the recirculation exhaust gas control catalyst, while preventing the clogging of the exhaust gas recirculation passage, and additionally accomplishes the switching from the second combustion to the first combustion at an early time.
In the first mode of the invention, it is possible to adopt a construction wherein, when the second combustion is performed at the start-up of the engine, the engine performs a main fuel injection near a compression top dead center, and an additional fuel injection at a timing different from a timing of the main fuel injection. The engine further reduces an amount of an intake air in order to perform the combustion in which the amount of the hydrocarbon in the exhaust gas increases, and the temperature of the exhaust gas discharged from the combustion chamber becomes relatively high.
According to this mode, during the second combustion at the startup, the engine performs the main fuel injection near the compression top dead center, an additional fuel injection at a timing different from the timing of the main fuel injection, and also reduces the amount of intake air. That is, in addition to the main injection in the vicinity of the compression top dead center, the injection at the timing that is different from the timing of the main injection is performed, the amount of unburned hydrocarbon in exhaust gas can be increased. Furthermore, due to the post-combustion of the unburned hydrocarbon, the temperature of exhaust gas discharged from the combustion chamber can be made relatively high. Moreover, the reduction in the amount of intake air also raises the temperature of exhaust gas discharged from the combustion chamber to a relatively high temperature level.
In the first mode of the invention, it is also possible to adopt a construction wherein the engine gradually increases the amount of the recirculation exhaust gas from zero when the temperature of the exhaust gas has reached a temperature that is sufficiently high to warm up the recirculation exhaust gas control catalyst.
According to this mode, when the exhaust gas temperature becomes sufficiently high for warming up the recirculation exhaust gas control catalyst, the amount of recirculation exhaust gas is gradually increased from zero. That is, while the exhaust gas temperature is still low and the recirculation exhaust gas control catalyst is not able to remove hydrocarbon from recirculation exhaust gas, the amount of recirculation exhaust gas is controlled to zero. After the exhaust gas temperature becomes high and the recirculation exhaust gas control catalyst becomes able to remove hydrocarbon from recirculation exhaust gas, the amount of recirculation exhaust gas is gradually increased from zero. Therefore, the engine reliably prevents problems that occur when the recirculation exhaust gas control catalyst is not able to remove hydrocarbon from recirculation exhaust gas, and recirculation exhaust gas is caused to flow through the exhaust gas recirculation passage, thus resulting in the clogging of the exhaust gas recirculation passage.
In the first mode of the invention, it is also possible to adopt a construction wherein, when the recirculation exhaust gas control catalyst has been warmed up, the second combustion is switched to the first combustion.
According to this mode, the combustion is switched from the second combustion to the first combustion when the warm-up of the recirculation exhaust gas control catalyst is completed. That is, when the warm-up of the recirculation exhaust gas control catalyst is completed and the recirculation exhaust gas control catalyst is able to remove a large amount of hydrocarbon, the second combustion is switched to the first combustion, and the amount of recirculation exhaust gas is increased in a stepped-up manner. Therefore, the engine is able to prevent problems that occur when the warm-up of the recirculation exhaust gas control catalyst has not been completed, and the recirculation exhaust gas control catalyst is not able to remove a large amount of hydrocarbon, thus causing a large amount of recirculation exhaust gas to flow through the exhaust gas recirculation passage and clog the exhaust gas recirculation passage.